Are you familiar with the reason the concept of depreciation exists in tax law? Because profits are what the government is trying to tax. Contra your point 2, it makes no sense to tax revenue in a way that ignores expenses. You'd be taxing two businesses the same, whether or not those revenues were just eaten by expenses.
But once you're taxing profits, you need a sane model of what constitutes business profits, and which handles more than the (very atypical) case of "buy a block of stuff, then sell it for more". At any given moment, a business has inventory and capital equipment, which is not completely used up, nor sold. How should that affect profit?
When you say "don't allow depreciation writeoff", then you're saying one of two things, neither of which maps to a good model of "how much profit is this business making".
You're saying either:
1) Any capital good should be booked immediately as a pure expense. That would imply that businesses can forever defer taxable profits simply by spending all profits on such equipment. "Oops, don't owe taxes -- again -- because we bought another robot. Sorry!"
2) Any capital good should be completely non-deductible as an expense. This would mean that one class of expense somehow "doesn't count" merely because it happens over years rather than the moment you buy it (e.g. wear-down of a saw vs purchase of electricity).
Depreciation schedules do not exist as some giveaway-subsidy for capital good purchases, but to recognize the economic reality that the truth is somewhere in the middle; that a capital (durable) good does not immediately decrease profits, but does function as an expense over a longer span of time.
In an ideal world, we would have an auction to get the market value of each used capital good to know how much value the business lost as the capital good lost its value. But this would be horribly expensive and convoluted, so businesses are allowed to assume a certain schedule. The harm of such an approximation is minimal; any discrepancy between the schedule value vs the true market value is realized as income or loss when the good is sold.
tl;dr: Depreciation is not a subsidy, but a recognition of the true effect of capital good usage on a business's book value and therefore taxable quarterly profits.
Late edit: Disclaimer: not an accountant, just my understanding of the logic behind depreciation in tax law.